Building a catapult sounds like something that should require a castle, a moat, and at least one suspiciously dramatic medieval helmet. Thankfully, this version needs none of those things. This guide shows you how to build a small, safe tabletop catapult using everyday craft supplies like popsicle sticks, rubber bands, a plastic spoon or bottle cap, and soft projectiles such as cotton balls or pom-poms.
The goal is not to build a backyard siege machine. The goal is to make a fun STEM project that teaches force, motion, energy transfer, launch angle, measurement, and the engineering design process. In other words, you get to launch a cotton ball across the table and call it science. That is a pretty good day.
This simple catapult project works well for students, parents, teachers, homeschool lessons, science fairs, rainy afternoons, and anyone who has ever looked at a rubber band and thought, “Surely this could do something more exciting.” By the end, you will know how to build a catapult, how to test it, how to improve it, and how to avoid turning your living room into a tiny disaster zone.
What Kind of Catapult Are We Building?
This guide focuses on a mini popsicle stick catapult, sometimes called a craft stick catapult or tabletop catapult. It uses a lever arm and rubber bands to store and release energy. When you pull the arm back, energy is stored in the stretched rubber bands and bent materials. When you let go, that stored energy becomes motion, launching a lightweight object forward.
This design is popular in classrooms because it is inexpensive, quick to assemble, and easy to modify. It also makes physics feel less like a textbook and more like a tiny launch tournament. The project is best used with soft, lightweight objects only. Cotton balls, pom-poms, mini marshmallows, or crumpled paper balls are ideal. Do not use rocks, coins, batteries, hard candy, sharp objects, or anything that could hurt someone or damage property.
Materials You Will Need
Before you begin, gather your supplies. A clean table, desk, or floor space will make the project easier. If you are doing this with kids, adult supervision is recommended, especially when cutting, gluing, or using small parts.
Basic Supplies
- 8 to 10 jumbo craft sticks or popsicle sticks
- 4 to 6 sturdy rubber bands
- 1 plastic spoon or 1 plastic bottle cap
- Glue, tape, or a low-temperature glue gun with adult help
- Cotton balls, pom-poms, mini marshmallows, or crumpled paper balls
- Ruler or measuring tape
- Notebook or printable data chart
- Markers or stickers for decoration, if your catapult needs personality
Optional Testing Supplies
- Paper cups for targets
- Masking tape to mark a launch line
- Protractor to measure launch angle
- Small sticky notes for recording trial numbers
- Different soft projectiles for comparison
Safety First: Keep It Fun, Not Frightening
A small catapult can be safe and educational when used correctly. Set clear rules before launching anything. Only launch soft objects. Keep the catapult pointed away from people, pets, screens, windows, lamps, and snacks you still plan to eat. Hold the base steady when releasing the lever arm so the catapult does not flip over. Launch in an open area, and stop immediately if the rubber bands crack, snap, or look worn out.
This project is designed for gentle STEM exploration. Bigger does not mean better. A catapult that launches a cotton ball accurately at a paper cup is much more useful for learning than one that scares the dog and knocks over a water bottle. Science should create “aha!” moments, not “uh-oh” moments.
How to Build a Catapult Step by Step
Follow these instructions to build a sturdy tabletop catapult. You can complete the basic model in about 15 to 30 minutes, depending on how much decorating, adjusting, and “just one more test” happens along the way.
Step 1: Make the Base Stack
Stack 6 to 8 craft sticks directly on top of each other. Wrap a rubber band tightly around one end of the stack. Then wrap another rubber band tightly around the other end. This creates the raised base that gives your catapult its springy support.
The thicker the stack, the higher the launching arm will sit. A taller stack usually gives the arm more room to move, but it can also make the catapult less stable if the base is too narrow. For beginners, 7 or 8 sticks is a good starting point.
Step 2: Create the Launching Arm
Take two craft sticks and stack them together. Wrap a rubber band around one end only. The opposite end should open like a pair of tongs. This is the lever arm, which will move up and down when you launch your soft projectile.
If you are using a plastic spoon, tape or glue the spoon handle to the top stick, with the bowl of the spoon facing upward. If you are using a bottle cap, glue the cap near the front end of the top stick. This cap becomes the small basket that holds the cotton ball or pom-pom.
Step 3: Insert the Base Stack
Open the two-stick lever arm slightly and slide the thick base stack between the two sticks, close to the rubber-banded end of the lever arm. The base stack should act like a wedge, holding the two arm sticks apart.
Move the base stack forward or backward to change how the catapult behaves. If the stack is closer to the rubber-banded hinge, the arm may have more travel. If it is farther forward, the arm may feel stiffer. This is one of the easiest ways to experiment with design changes.
Step 4: Secure the Crossing Point
Wrap another rubber band around the point where the lever arm and base stack cross. This keeps the pieces from sliding apart. The rubber band should be snug, but not so tight that the launching arm cannot move.
Test the motion by gently pressing down on the spoon or cap and letting it rise back up. It should spring upward smoothly. If it wobbles like a baby giraffe on a tile floor, adjust the rubber bands and straighten the sticks.
Step 5: Add the Projectile Holder
If you have not already attached the spoon or bottle cap, do that now. A plastic spoon is convenient because it naturally holds rounded objects. A bottle cap works well for cotton balls and pom-poms because it keeps the projectile centered.
Let glue dry fully before testing. Launching too soon is tempting, but wet glue has the structural confidence of pudding. Give it time to set so your catapult does not dismantle itself during the grand opening ceremony.
Step 6: Set Up a Launch Zone
Place a strip of masking tape on the table or floor as your launch line. Put a paper cup, bowl, or taped square target a short distance away. Start close, about 1 to 2 feet, then increase the distance as your aim improves.
Use only one soft projectile at a time. Place it in the spoon or cap, press the arm down gently, aim toward the target, and release. Measure how far it travels. Record the result. Repeat at least three times so you can compare results instead of trusting one lucky launch.
How a Catapult Works
A catapult is a simple machine that uses stored energy to move an object. In this tabletop design, the rubber bands and bent craft sticks store elastic potential energy. When you release the arm, that energy changes into kinetic energy, which is the energy of motion.
The craft stick arm acts as a lever. The place where the arm pivots is called the fulcrum. Changing the fulcrum position changes how the catapult launches. Move the base stack slightly, and you change the length of the lever arm, the angle of release, and the amount of force transferred to the projectile.
Launch angle matters too. A low angle may send the cotton ball forward but not very far upward. A high angle may send it up dramatically but not far across the table. Somewhere in between is usually the sweet spot. Finding that sweet spot is the difference between “engineering” and “randomly flinging fluff,” although both can look suspiciously similar at first.
Testing Your Catapult Like an Engineer
Once your catapult works, the real fun begins. Engineers rarely build one version and declare victory forever. They test, measure, improve, and test again. Your catapult is a prototype, which is a fancy word for “the first version that will probably need help.”
Try These Experiments
- Distance test: Launch the same cotton ball three times and measure how far it travels.
- Accuracy test: Place a cup or paper target nearby and count how many launches hit the target out of ten attempts.
- Projectile test: Compare cotton balls, pom-poms, mini marshmallows, and paper balls.
- Lever test: Move the base stack forward or backward and record how the distance changes.
- Rubber band test: Try a thicker or thinner rubber band and observe the difference.
- Angle test: Use a protractor to estimate the launch angle and compare results.
Record Your Data
A simple chart can turn this project into a strong science activity. Create columns for trial number, projectile type, launch distance, target result, and notes. For example, you might discover that a pom-pom flies farther than a cotton ball, but the cotton ball lands more accurately. That is a useful result, not a failure.
Good engineering is not about guessing perfectly. It is about noticing what happened, asking why it happened, and making a smarter version next time. Your notebook may not look glamorous, but it is where the actual learning happens.
Troubleshooting Common Catapult Problems
The Catapult Falls Over
If the catapult tips forward during launch, the base may be too narrow or too light. Add a wider cardboard platform underneath and tape the craft stick base to it. You can also hold the back of the base gently while launching.
The Projectile Goes Straight Up
If your cotton ball launches almost vertically, the arm angle may be too steep. Move the stick stack slightly forward or reduce how far you pull the arm back. You want a smooth arc, not a dramatic elevator ride.
The Projectile Barely Moves
If the launch is weak, check the rubber bands. They may be too loose, too old, or not positioned well. Also make sure the spoon or bottle cap is firmly attached. A wobbly holder wastes energy.
The Catapult Is Inconsistent
Inconsistent launches usually come from inconsistent pulling. Mark a pull-back line with a small piece of tape on the catapult arm. Pull to the same point each time. This makes your tests more reliable and helps you compare changes fairly.
Easy Catapult Variations
After building the basic version, try a few variations. Keep everything small, soft, and safe.
Plastic Spoon Catapult
This version uses a plastic spoon as the launching basket. It is easy to build and works well with mini marshmallows, pom-poms, and paper balls. The spoon gives the projectile a curved seat, which helps keep it from rolling off before launch.
Bottle Cap Catapult
This version uses a bottle cap glued to the launch arm. It is compact, neat, and excellent for cotton balls. The cap also makes the design look more like a tiny engineering device and less like a spoon having a midlife crisis.
Target Game Catapult
Set up paper cups at different distances and assign point values. A cup close to the launch line might be worth 1 point, while a farther cup might be worth 5 points. This turns the activity into a game while still teaching accuracy, precision, and measurement.
Science Fair Catapult
For a science fair, choose one variable to test. Do not change everything at once. You might ask, “How does projectile mass affect launch distance?” or “How does the position of the fulcrum affect accuracy?” Build a chart, repeat each trial, and explain your results clearly.
What You Learn From Building a Catapult
A catapult may look like a simple craft, but it teaches several important STEM ideas. You learn how energy can be stored and released. You see how force affects motion. You explore how mass changes the way an object travels. You discover that small design changes can produce big differences in performance.
You also practice the engineering design process: ask a question, imagine solutions, plan a design, build a prototype, test it, improve it, and test again. That process is useful far beyond catapults. It applies to bridges, robots, apps, bicycles, kitchen gadgets, and almost every invention that did not work perfectly on the first try.
Best Tips for a Better Catapult
- Use fresh rubber bands because old ones lose stretch and may snap.
- Keep the base stable before trying to increase launch distance.
- Use the same projectile for fair testing.
- Measure from the same launch line every time.
- Change only one variable per experiment.
- Record results instead of relying on memory.
- Decorate after testing, unless style points are part of your scientific method.
Experiences and Practical Lessons From Building a Catapult
The first thing you learn when building a catapult is that simple projects are only simple after they work. At the beginning, a few craft sticks and rubber bands look harmless. Five minutes later, you may be holding a crooked little contraption that launches a cotton ball backward. This is normal. In fact, it is one of the best parts of the project. A catapult teaches patience because it rewards small adjustments more than big dramatic changes.
One useful experience is discovering how much stability matters. Many beginners focus only on making the projectile fly farther. They add tighter rubber bands, pull the arm back harder, or stack more sticks under the lever. Then the entire catapult jumps, flips, or twists during launch. The lesson is clear: power without control is not good engineering. A wider base, a steady launch line, and a balanced arm often improve results more than simply adding more force.
Another lesson comes from testing different projectiles. A mini marshmallow may look like a champion because it has a nice shape, but it can bounce unpredictably. A cotton ball is soft and safe, but it may be so light that air resistance slows it down. A pom-pom often gives a satisfying launch, but different sizes behave differently. This is where the project becomes more than a craft. You begin to notice mass, shape, friction, and air resistance in action.
The best catapult builders also learn to respect repeat testing. One launch tells you what happened once. Three launches begin to tell you what usually happens. Ten launches can reveal a pattern. If your catapult hits the target once, celebrate. If it hits the target seven times out of ten, you have a design worth bragging about. Accuracy is often more impressive than distance, especially when your target is a paper cup and your audience is pretending not to be competitive.
Working in a group adds another layer of learning. One person may want a stronger rubber band. Another may want a longer lever arm. Someone else may care mostly about decorating the catapult with flames, lightning bolts, or a name like “The Fluff Launcher 3000.” These different ideas can actually improve the final design if the group tests them fairly. The project becomes a lesson in communication, compromise, and shared problem-solving.
Finally, building a catapult is a reminder that failure is data wearing a fake mustache. A weak launch tells you something. A sideways launch tells you something. A catapult that falls apart tells you a lot, although it may do so with unnecessary drama. Every result gives you a clue about what to change next. That is why this project is so valuable for STEM learning. It is hands-on, slightly silly, easy to repeat, and full of real science hiding inside a playful activity.
Conclusion
Learning how to build a catapult is one of the easiest ways to turn common household materials into a meaningful STEM lesson. With craft sticks, rubber bands, and a soft projectile, you can explore force, motion, potential energy, kinetic energy, launch angle, accuracy, and engineering design. The project is simple enough for beginners, but flexible enough for deeper experiments and science fair questions.
The key is to keep it safe, small, and thoughtful. Use soft projectiles, test in an open area, measure your results, and improve one variable at a time. Your first catapult does not have to be perfect. It only has to teach you something. And if it also launches a cotton ball into a paper cup while everyone cheers like you just landed a spacecraft, that is a bonus.
